North Korea stages 'largest ever' live-fire drill: KCNA

North Korean troops, watched by leader Kim Jong-un, have staged their largest-ever live-fire drill, vowing to turn South Korea's capital into a sea of flames and ashes, Pyongyang's state media reported Friday.

The drill involved more than 100 pieces of North Korea's long-range artillery and other weapons, the North's official Korean Central News Agency (KCNA) said. There was no mention of when and where the gunnery exercise took place.

South Korean military officials said it appeared to have been staged near the northeastern port city of Wonsan on Thursday.

KCNA said the drill was the "largest-ever" of its kind and stimulated a concerted attack on the office of South Korean President Park Geun-hye and other key locations in Seoul.

North Korea's powerful artillery will respond with a "merciless retaliatory" strike to any provocation from South Korea, its defense minister Pak Yong-sik said in a speech cited by KCNA.

Pak warned South Korea would see its capital "completely devastated into ashes", it said.